Stem cells are critical for organ development and tissue homeostasis. Their capacity to divide asymmetrically to produce both stem cells and differentiated daughters allows for replacement of dead and dying cells within a tissue. While maintenance of stem cells in fully formed organs is controlled by their microenvironment, or stem cell niche, mechanisms controlling stem cell development remain less clear. Indeed, the dramatic changes in cell signaling, migration and morphology that accompany organogenesis in many organisms make a comprehensive understanding of these mechanisms difficult. Thus, studies in highly tractable systems are required to gain a thorough understanding of stem cell development during organogenesis. Drosophila testes are among the most thoroughly characterized systems for studying stem cell behavior. In adult flies, sperm- producing germline stem cells (GSCs) and somatic cyst stem cells (CySCs) whose progeny nurture spermatogenesis, cohabit a discrete stem cell niche at the testis apex. Work by the Wawersik lab has shown that functional, asymmetrically dividing GSCs are first established from primordial germ cell (PGCs) at the end of embryogenesis. This process is coordinated by formation of the stem cell niche, which includes newly established CySCs as well as somatic hub cells to which GSCs and CySCs become docked. With the timing of stem cell establishment characterized, Drosophila testes are an ideal system to study mechanisms controlling stem cell development during organogenesis. Here, we propose experiments aimed at characterizing the fate and morphogenesis of somatic precursor cells that give rise to the testis stem cell niche (Aim 1), as well as determining mechanisms controlling these processes (Aims 2 & 3).